We use a sound meter and human judgment to rate noise.Photograph by Michael Smith

All of the 35 window air conditioners we tested, even a $99 unit (available to subscribers), proved excellent at cooling. But some less expensive models might make you lose your cool because
they're noisy or don't work well on the hottest days and nights.

The pinging of water hitting the condenser, the gurgling of the refrigerant moving through the evaporator, and the chatter
of the compressor are normal operating sounds, according to some manufacturers. We listened and scored each unit's noise on
the low and high settings in our test chamber, which tends to amplify sounds because there are no soft surfaces like beds
or sofas to help absorb them. The Ratings (available to subscribers) reflect how quiet each unit is compared with the others in our tests. None of the air conditioners
are silent, but an Excellent or Very Good score means you might hear the fan running but you'll barely notice the compressor.

On the hottest days and nights, utility companies often compensate for high electrical demand by reducing voltage. We simulate
those brownout conditions. Most A/Cs do fine, but some, like the large Sharp AF-S120 and the small $99 Haier HWF05XC7-T (available to subscribers), couldn't handle the lower voltage. Months of testing revealed three CR Best Buys, eight other
Recommended models, and more findings:

Eco-friendlier A/Cs work well

Air conditioners made in 2010 must use a refrigerant that does not deplete the ozone. Most makers have switched to R-410A.
Performance wasn't affected in any of the models we tested. Given last year's cooler summer temperatures, you'll still find
on store shelves older models that use the less environmentally friendly refrigerant. Look at the boxes; some note the new
refrigerant or have a green leaf or symbol. We footnoted models using R-410A in our Ratings (available to subscribers).

Save energy and money

Energy Star-qualified models are claimed to use at least 10 percent less energy than standard models and about 25 percent
less juice than models made a decade ago. Trim energy costs by using the timer to turn on the A/C just before you arrive home.
Don't lower the set temperature as soon as you turn on the unit. It doesn't cool the room faster, and it will use more energy.
A higher fan speed also uses more energy but not much. To keep your unit running efficiently, vacuum, wash, and dry filters
monthly or as needed.